Clinical determinants and prognostic significance of hypocapnia in acute heart failure

Abstract

The aim of this research was to examine the prevalence of hyperventilation (defined by pCO₂ value) among acute heart failure (AHF) patients and to link it with potential triggers and prognosis. All patients underwent dyspnea severity assessment and capillary blood examination on hospital admission and during hospitalization. Out of 241 AHF patients, 57(24%) were assigned to low pCO₂ group (pCO₂ ≤ 30 mmHg) and 184 (76%) to normal pCO₂ group (pCO₂ > 30 mmHg). Low pCO₂ group had significantly lower HCO₃^- (22.3 ± 3.4 vs 24.7 ± 2.9 mmol/L, p < 0.0001) and significantly higher lactate level (2.53 ± 1.6 vs 2.14 ± 0.97 mmol/L, p = 0.03). No differences between groups were observed in respect to the following potential triggers of hyperventilation: hypoxia (sO₂ 92.5 ± 5.2 vs 92 ± 5.6% p = 0.57), infection (CRP 10.5[4.9-26.4]vs 7.15[3.45-17.35] mg/L, p = 0.47), dyspnea severity (7.8 ± 2.3vs 8.0 ± 2.3 points, p = 0.59) and pulmonary congestion (82.5 vs 89.1%, p = 0.19), respectively. Low pCO₂ value was related to an increased 4-year all-cause mortality hazard ratio (HR) (95% CI) 2.2 (1.3-3.6); p = 0.002 and risk of death and of rehospitalization for HF, HR (95% CI) 2.0 (1.3-3.0); p = 0.002. Hyperventilation is relatively frequent in AHF and is related to poor prognosis. Low pCO₂ was not contingent on expected potential triggers of dyspnea but rather on tissue hypoperfusion.

Figure 1

The prevalence of low pCO₂ (≤ 30 mmHg) in AHF patients during hospital stay.

Figure 2

Comparison of dyspnea perception between patient with different pCO₂ level. Assessment of dyspnea perception was performed with the use of a self-reported 10-point Likert scale. Red—patients with normal pCO₂ (> 30 mmHg). Blue—patients with low pCO₂ (≤ 30 mmHg).

Figure 3

Kaplan–Maier curves for death or heart failure rehospitalization (whichever occurred first) by pCO₂ level on admission. (a) Death analysis. Log rank p = 0.002. Red line—patients with normal pCO₂ value (> 30 mmHg). Blue line—patients with low pCO₂ value (≤ 30 mmHg). (b) Death or heart failure rehospitalization (whichever occurred first) by pCO₂ level on admission. Log-rank p = 0.002. Red line—patients with normal pCO₂ value (> 30 mmHg). Blue line—patients with low pCO₂ value (≤ 30 mmHg).